Hormones and Homeostatic Mechanisms 175 



older animals. In younger animals it increased renal losses, 

 which thus nearly reached the levels of the older controls. 

 In 33-day-old animals water losses decreased after cortexone. 

 The higher dose, however, had no effect on renal losses of 

 water in 23-day-old animals, whereas in 33-day-old rats it 

 further decreased renal losses. These doses, however, are 

 probably toxic. Sodium losses were never significantly 

 altered by either dose of cortexone in the younger group. In 

 33-day-old animals they changed in direct proportion to the 

 dose used. In both age groups cortexone decreases renal 

 potassium losses significantly. 



Thus corticoids have a different effect on the elimination 

 of water and electrolytes after a water load in infant rats that 

 have not yet reached the age at w^hich they are normally 

 weaned, than they have in older animals. The opposite effects 

 in 23-day-old animals, depending on the dose used, indicate 

 that these hormones cause changes that mutually interfere 

 with each other. 



We attempted to determine whether in addition to the 

 pharmacodynamic effect of these hormones there is also an 

 effect on the regulation of adrenal activity. 



The weight of the adrenals of animals receiving cortisone or 

 cortexone, as indicated above, dropped to about the same 

 extent in both 23- and 33-day-old animals. Simultaneous 

 administration of ACTH in amounts usually sufficient to 

 maintain adrenal weights of hypophysectomized animals 

 (0-2 i.u. per animal) prevents adrenal atrophy in both 

 groups. This reaction is less obvious on histological studies. 

 Fig. 5 shows microphotographs of the adrenal cortices of 23- 

 and 33-day-old animals (controls; after cortisone [0-25 mg./ 

 lOOg./day] ; after ACTH [0 • 2 i.u. animal/day] ; and after simul- 

 taneous administration of cortisone and ACTH). Preparations 

 were stained with Sudan Black so that both the width of the 

 cortex and the sudanophil layers can be seen. After ACTH 

 there are no obvious changes in the width of the cortex and 

 the sudanophil layer. After cortisone and cortisone plus 

 ACTH differences are evident. This is even more apparent 



